Patent GB-873609-A (GB)
Title: Process for the removal of hydrogen cyanide from coke-oven gas
IPC: C10K1/16
Filed: 1957-08-08
Abstract: HCN is removed from coke oven gas or impurity concentrates therefrom by scrubbing with a medium containing a saturated aliphatic ketone, or aldehyde, or an epoxide, or mixtures thereof and having a pH above 7, or in the range 2-5.  The pH of the medium may be controlled by the addition of a small amount of dilute acid, when HCN may be separated by distillation, or small amounts of dilute aqueous alkali metal hydroxide or carbonate, when HCN may be separated by distillation after acidification. When cyanhydrins are desired the medium should include an ionised salt of HCN, either added as aqueous alkali metal cyanide, or produced in situ, which also produces an alkaline medium. Cyanhydrin may be separated by fractionation after acidification. Suitable scrubbing media are acetone, methyl propyl ketone, diethyl ketone, paraformaldehyde, propionaldehyde, or ethylene oxide, and scrubbing temperatures may be 5-20 DEG C. under elevated pressure, if desired.  The NH3 content of the gas before scrubbing should be reduced to less than 0.5 grm./c.m. by scrubbing with aqueous H2SO4 followed by drying over CaCl2 and the oxygen content should be reduced below 2% vol. Cyanhydrins may be purified by rectification in vacuo.  Should the cyanhydrin not be formed, the vapours from distillation of the medium are condensed, and passed into the scrubbing medium containing an ionisable salt of HCN. Should cyanhydrin formation still fail, the medium is redistilled in the alkaline state, and the distillate is introduced into the medium containing an aqueous alkali metal cyanide.ALSO:Hydrogen cyanide is removed from coke oven gas or impurity concentrates therefrom by scrubbing with a medium containing a saturated aliphatic ketone, or aldehyde, or an epoxide, or mixtures thereof and having a pH above 7, or in the range 2-5. The pH of the medium may be controlled by the addition of a small amount of dilute acid, when HCN is separated by distillation, or small amounts of dilute aqueous alkali metal hydroxide or carbonate, when HCN is separated by distillation after acidification.  When cyanhydrin is desired the medium should include an ionised salt of HCN either added as aqueous alkali metal cyanide, or produced in situ, which also produces an alkaline medium. Cyanhydrin may be separated by fractionation after acidification. Suitable scrubbing media are acetone, methyl propyl ketone, diethyl ketone, paraformaldehyde, propionaldehyde, or ethylene oxide, and scrubbing temperatures may be 5-20 DEG C. under elevated pressure, if desired.  The ammonia content of the gas before scrubbing should be reduced to less than 0.5 grms/cm. by scrubbing with aqeous H2SO4 followed by drying over CaCl2 and the oxygen content should be reduced below 2% vol. Cyanhydrins may be purified by rectification in vacuo.  Should the cyanhydrin not be formed, the vapours from distillation of the medium are condensed, and passed into the scrubbing medium containing an ionisable salt of HCN.  Should cyanhydrin formation still fail, the medium is redistilled in the alkaline state, and the distillate is introduced into the medium containing an aqueous alkali metal cyanide.